Process and apparatus for moulding and curing tyres

Abstract

A process for molding and curing tires, includes introducing a green tire into a curing mold, the mold including a first sidewall plate and a second sidewall plate, a ring of circumferential sectors circumscribing a mold cavity, an expandable bladder delimited by a membrane, and at least one bead molding ring which is movable between a first contracted operating position and a second extended operating position; and molding and curing the green tire in the curing mold; and between introducing the green tire and molding and curing it, the process includes extending the at least one bead molding ring from the first contracted operating position to the second extended operating position; forming a circumferential bearing surface which bears against a first axially inner surface portion of a first annular fixing structure of the green tire; pressing a second axially inner surface portion of the first annular fixing structure by expanding the membrane at a pre-molding pressure which is lower than a molding pressure, so as to bring the first annular fixing structure into contact with the first sidewall plate thus shaping an axially outer surface portion of the first annular fixing structure by means of the first sidewall plate and shaping the first axially inner surface portion of the first annular fixing structure by means of the circumferential surface of the at least one bead molding ring.

The invention claimed is: 
     
       1. A process for moulding and curing a tyre, the process comprising:
 introducing a green tyre into a curing mould, said mould comprising a first sidewall plate and a second sidewall plate, a ring of circumferential sectors circumscribing a mould cavity, an expandable bladder delimited by a membrane, and a first and a second bead moulding ring each movable between a first contracted operating position and a second extended operating position, the second bead moulding ring comprising a plurality of petal-like elements; and 
 moulding and curing said green tyre in said curing mould, 
 wherein between introducing said green tyre and moulding and curing said green tyre:
 extending the first bead moulding ring from said first contracted operating position to said second extended operating position, forming a first circumferential bearing surface which bears against a first axially inner surface portion of a first annular fixing structure of said green tyre; 
 extending the second bead moulding ring to form a second circumferential bearing surface which bears against a first axially inner surface portion of a second annular fixing structure of the green tyre, wherein extending the second bead moulding ring includes rotating the petal-like elements with respect to each other; 
 making the second sidewall plate bear against the second annular fixing structure; and 
 pressing a second axially inner surface portion of said first annular fixing structure by expanding said membrane at a pre-moulding pressure which is less than a moulding pressure, whereby said first annular fixing structure is brought into contact with said first sidewall plate, thus shaping an axially outer surface portion of said first annular fixing structure using the first sidewall plate and shaping said first axially inner surface portion of said first annular fixing structure using the first circumferential surface of the first bead moulding ring. 
 
 
     
     
       2. The process according to  claim 1 , wherein:
 the first bead moulding ring comprises a plurality of sectors; and 
 said second axially inner surface portion of said first annular fixing structure is contiguous and radially external to said first axially inner surface portion of said first annular fixing structure which bears against said sector of the first bead moulding ring. 
 
     
     
       3. The process according to  claim 1 , wherein moulding and curing said green tyre comprises increasing said pre-moulding pressure to said moulding pressure. 
     
     
       4. The process according to  claim 1 , wherein said pre-moulding pressure is in a range from approximately 0.1 to approximately 2 bars. 
     
     
       5. The process according to  claim 1 , wherein said pre-moulding pressure is in a range from approximately 0.2 to approximately 0.8 bar. 
     
     
       6. The process according to  claim 1 , wherein the first bead moulding ring comprises a plurality of alternating sectors, and extending the first bead moulding ring comprises:
 axially translating said sectors of the first bead moulding ring toward said first sidewall plate; and 
 radially extending the first bead moulding ring from said contracted operating position with retracted sectors, having a first diameter smaller than a circumference of said first annular fixing structure, to said second extended operating position of the first bead moulding ring with extended sectors, forming said first circumferential surface having a second diameter which is greater than a diameter of said first annular fixing structure, so as to retain said first annular fixing structure between said first circumferential surface and said first sidewall plate. 
 
     
     
       7. The process according to  claim 1 , wherein extending the second bead moulding ring and making the second sidewall plate bear against the second annular fixing structure occur between extending the first bead moulding ring and pressing the second axially inner surface portion of said first annular fixing structure. 
     
     
       8. The process according to  claim 1 , wherein pressing the second axially inner surface portion of said first annular fixing structure comprises:
 pressing a second axially inner surface portion of said second annular fixing structure by expanding said membrane at said pre-moulding pressure in such a way that said second annular fixing structure is brought into contact with said second sidewall plate, thereby shaping an axially outer surface portion of said second annular fixing structure by means of said second sidewall plate and shaping said first axially inner surface portion of said second annular fixing structure by means of said second bead moulding ring. 
 
     
     
       9. The process according to  claim 1 , wherein:
 said mould comprises a telescopic central body into which said green tyre is inserted and on which said expandable bladder is fixed, said opposing ends of said telescopic central body being fixed to said first and said second bead moulding rings, and 
 extending said first bead moulding ring and said second bead moulding ring is preceded by:
 telescopically elongating or shortening said telescopic central body according to the axial dimension of said green tyre so as to place said second bead moulding ring in the contracted position at the position of said second annular fixing structure of said green tyre. 
 
 
     
     
       10. The process according to  claim 1 , wherein the petal-like elements of the second bead moulding ring have substantially identical shapes. 
     
     
       11. The process according to  claim 1 , wherein extending the second bead moulding ring includes moving the petal-like elements from a first contracted operating position in which the petal-like elements are partially superimposed to a second operating position whereby the petal-like elements are contiguous and form the second circumferential bearing surface. 
     
     
       12. The process according to  claim 11 , wherein, in the second operating position, the second circumferential bearing surface is continuous. 
     
     
       13. The process according to  claim 11 , wherein the petal-like elements are in the second operating position during the moulding and curing of the green tyre. 
     
     
       14. The process according to  claim 1 , wherein the second bead moulding ring is extended during the moulding and curing of the green tyre. 
     
     
       15. The process according to  claim 1 , further including extending a telescopic central element on which the green tyre is fitted and to which the membrane delimiting the expandable bladder is fixed, an amount of extension of the telescopic central element being based on a size of the green tyre. 
     
     
       16. The process according to  claim 15 , wherein:
 the telescopic central element comprises at a first end thereof, a first platen, to which the first bead moulding ring is fixed, and, at a second opposing end thereof, a second platen, to which the second bead moulding ring is fixed; and 
 extending the telescopic central element includes adjusting a distance between the first platen and the second platen. 
 
     
     
       17. The process according to  claim 1 , wherein:
 the first bead moulding ring comprises a plurality of sectors divided into a first plurality and a second plurality, each sector of the first plurality alternating circumferentially with a sector of the second plurality; and 
 extending the first bead moulding ring from the first contracted operating position to the second extended operating position includes moving the plurality of sectors from a contracted position to an extended position. 
 
     
     
       18. The process according to  claim 17 , wherein the sectors of the first plurality are radially divergent, and the sectors of the second plurality are radially convergent. 
     
     
       19. The process according to  claim 17 , wherein extending the first bead moulding ring from the first contracted operating position to the second extended operating position includes forming a continuous circumferential surface and positioning a radially outer edge of the first plurality substantially coaxial with a radially inner edge of the second plurality. 
     
     
       20. The process according to  claim 19 , wherein the radially outer edge of the first plurality and the radially inner edge of the second plurality are offset in the first contracted operating position of the first bead moulding ring. 
     
     
       21. The process according to  claim 1 , wherein extending the first bead moulding ring from the first contracted operating position to the second extended operating position includes axially inserting a cone-shaped element of the first bead moulding ring into a centre of the first bead moulding ring.